Alcator C-Mod Weekly Highlights
			October 20, 1997
 

The maintenance period on Alcator C-Mod continued last week.  Re-assembly
of the alternator,  work on the DNB and RF systems, and data analysis from
the last run period also proceeded.

All rotating components of the alternator including bearings, brushes,
and couplings to flywheel and drive motor have been re-installed.  MD&A, the
contractor responsible for the rewind and re-assembly has now finished
all assembly tasks.  As soon as re-installation of the instrumentation is
complete, MD&A will return to help commission the alternator and complete
rotor balancing.  A review of the alternator instrumentation, fault
systems, interlocks, and coordination was held this week in preparation
for restart.

FMIT#1 and #2's power feedback circuits have been adjusted to allow
the RF power to be modulated at up to 1 kHz.  The overshoot problem reported
here last week was caused by a unneeded filter in the feedback circuit.
Work on FMIT#3 and #4 continues.  New wiring tables have been made, and
documentation of the system has begun.  Work on the control wiring is
progressing.  The Uptegraff #4 power supply has returned from the manufacturer
where it was repaired.  The problem was identified as a poor connection on
one of the three secondary legs.  In addition, the diode stack and filter
capacitor were replaced.  It has been reconnected and is awaiting
testing.

Construction of the high voltage, low capacitance transmission line for the
DNB continued with assembly of duct sections and installation of internal
insulating duct supports.  Commissioning of the accelerator power supply
began.  A procedure was devised for conditioning the oil in this supply to
bring its insulation to the required specification.  An isolation amplifier
was tested and selected for the secondary emission measurement that is one
of the beam performance monitors.  The suppressor switch -- recently
reconfigured -- and the snubber were located near their final positions in
the DNB test lab.  Dexter Beals of MTechnology Inc. joined the DNB team.
His first task is to complete  modifications to the modulator regulator that
are required for compatibility with the accelerator power supply.

Analysis of H-mode results from the last campaign continue. H-L transitions
have been examined for precursor-like signals on the magnetics.  Coherent
150 kHz signals were observed only on outboard coils, which might indicate
that the instability is localized to the outer edge.  A toroidal mode number
of 7 has been found.  The poloidal mode number could not be determined
because of poor signal coherence from the inboard coils.  Such characteristics
are very similar to those of Type III ELMs, and the triggering mechanism for
the H-L transition may be similar.

Dr. Stefano Bernabei visited from PPPL last week and discussed plans for
the lower hybrid system with the RF group.

Dave ONeill from PPPL was at MIT to participate in the alternator
instrumentation review.

Bruce Lipschultz was in Japan last week at an ITER Expert Group meeting